Floating offshore wind turbine

ABSTRACT

The present invention provides a floating offshore wind turbine capable of suppressing yawing of a nacelle caused by a gyro effect which is a cause of adverse influence of power generating efficiency of a wind turbine and endurance of devices thereof. The floating offshore wind turbine includes a rotor which is rotated by wind, a nacelle in which a rotation shaft of the rotor is accommodated, and a tower including a turning seated bearing which supports the nacelle such that the nacelle can turn with respect to a sea surface to exert a weathercock effect. The tower is provided with yawing suppressing means which suppresses yawing of the nacelle. According to this, it is possible to suppress the yawing of the nacelle generated by a gyro effect caused by yawing generated in the floating body by waves of the sea surface.

TECHNICAL FIELD

The present invention relates to a floating offshore wind turbinecapable of efficiently suppressing yawing (turning/oscillating motion)of a nacelle in which a rotation shaft of a rotor is accommodated andyawing of a floating body.

BACKGROUND TECHNIQUE

In conventional wind turbines, to change an orientation of a windturbine in accordance with change in a wind direction, an active controlapparatus which is combined with a wind direction sensor is used. Forexample, there is employed a configuration that a wind turbine is turnedby a power apparatus in accordance with a result of measurement of thewind direction sensor, and the wind turbine is held at a positionsuitable for the wind direction. To simplify a system of the entire windturbine, the active control apparatus is omitted in some cases. When theactive control apparatus is to be omitted, a rotation shaft of a rotorof the wind turbine is supported on a horizontal plane such that therotation shaft can freely turn, and the orientation of the wind turbineis changed by a weathercock effect to follow the change in the winddirection.

In the wind turbine, the rotor receives wind and rotates, therebygenerating electric power. If moment in a vertical direction is appliedto a rotation axis of rotation of the rotor, gyro moment is generated ina direction cross at right angles to both the direction of the momentand the rotation axis of the rotor by a so-called gyro effect. Forexample, in a floating offshore wind turbine provided on a floating bodywhich is floating in water, moment in the vertical direction isgenerated due to influence of waves. Hence, gyro moment is generated ina horizontal direction cross at right angles to the rotation axis ofrotation of the rotor by the gyro effect.

In a floating offshore wind turbine including the active controlapparatus, a nacelle is held by a floating body at a position matchingwith a wind direction. Therefore, rotation motion of the floating bodyrotating around a central axis of the floating body is generated by gyromoment caused by the gyro effect generated in the nacelle in which therotation shaft of the rotor of the wind turbine is accommodated. Here,since motion of waves is repetitive motion, the floating body movesrepetitively (yawing) together with the nacelle.

In a floating offshore wind turbine in which the active controlapparatus is omitted, a rotation shaft of a rotor of a wind turbine issupported such that the rotation shaft can freely turn with respect to afloating body. Hence, yawing of a nacelle is generated by gyro momentcaused by a gyro effect generated in the nacelle.

The present inventor found that moment caused by this gyro effect was acause of an adverse influence exerted on power generating efficiency ofthe floating offshore wind turbine and endurance of devices thereof.

To prevent vibration generated in a wind turbine apparatus, it isproposed to employ various configurations (patent documents 1 to 3).

Patent document 1 describes a wind turbine apparatus. The wind turbineapparatus includes, as an active control apparatus of a nacelle, awhirling driving source which whirls a platform supported on an upperend of a tower and fixing means in a whirling direction. In this windturbine apparatus, to suppress vibration generated in the tower or thelike by resonance of a blades and resonance wind speed, patent document1 describes a configuration that a vibration suppressing apparatus isprovided.

In a wind turbine, to attenuate vibration action in an edge direction ofblades of a rotor, patent document 2 describes a configuration thatoscillation action attenuating means is disposed in a nacelle.

In a wind turbine device, to prevent vibration from being transmitted toa nacelle frame through a speed increasing gear box and to preventvibration from being transmitted from the nacelle frame to the speedincreasing gear box, patent document 3 describes a configuration that avibration isolation damper is provided between the speed increasing gearbox and the nacelle frame.

PRIOR ART DOCUMENT Patent Document

-   [Patent Document 1 ]Japanese Patent Publication No. 2003-176774-   [Patent Document 2 ]Japanese translation of PCT International    Application, Publication No. 2002-517660-   [Patent Document 3 ]Japanese translation of PCT International    Application, Publication No. 2008-546948

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

Such a conventional wind turbine has a problem of vibration generated byrotation itself of the rotor and the like, but there are no conventionalwind turbines which focus attention on oscillation of a nacellegenerated by gyro moment caused by the gyro effect. Hence, the vibrationmotion suppressing means used in the wind turbine apparatuses describedin these patent documents can not prevent yawing of the nacelle and thefloating body generated by gyro moment caused by the gyro effect whenthe floating offshore wind turbine receives influence of waves.

Hence, it is an object of the present invention to provide a floatingoffshore wind turbine capable of preventing yawing of the nacelle andthe floating body generated by gyro moment caused by the gyro effect,and capable of suppressing adverse influence on power generatingefficiency of the wind turbine and endurance of devices thereof.

Means for Solving the Problem

A first aspect of the invention provides a floating offshore windturbine which generates electricity using a floating body as a portionof a structure body on ocean comprising a rotor which is rotated bywind, a nacelle in which at least a rotation shaft of the rotor isaccommodated, the structure body including turning means which supportsthe nacelle such that the nacelle can turn with respect to a watersurface, and yawing suppressing means which suppresses yawing of thenacelle with respect to the water surface and using a hydrodynamicdamper which suppresses yawing by mutual interference between a shape ora structure of the structure body and peripheral fluid as the yawingsuppressing means. According to this aspect, the yawing suppressingmeans can suppress the yawing of the nacelle caused by a gyro effect.Also, the yawing suppressing means can suppress yawing of the nacellewhich is induced by the gyro effect caused by pitching of the floatingbody on the ocean. According to the structure using this hydrodynamicdamper, resistance to yawing is varied by resistance to water of theunderwater hydrodynamic damper in accordance with a turning speed of thenacelle or the floating body, and it is possible to suppress the yawing.

According to a second aspect of the invention, in the floating offshorewind turbine of the first aspect, the nacelle is provided on a windwardside as compared with the rotor. According to this aspect, the nacellecan be turned with respect to a water surface by a so-called weathercockeffect, and an orientation of the rotation shaft can be made to conformto a wind direction.

According to a third aspect of the invention, in the floating offshorewind turbine of the second aspect, a coning angle is given to the rotor.According to this aspect, it is possible to further enhance theso-called weathercock effect.

According to a fourth aspect of the invention, in the floating offshorewind turbine of the first aspect, a hydraulic damper is further providedas the yawing suppressing means.

According to a fifth aspect of the invention, in the floating offshorewind turbine of the first aspect, a friction damper is further providedas the yawing suppressing means. If the hydraulic damper or the frictiondamper is used as the yawing suppressing means, resistance forsuppressing the yawing of the nacelle can be varied in accordance with aturning speed of the nacelle.

According to an eighth aspect of the invention, in the floating offshorewind turbine of the first aspect, the floating body is moored by mooringlines.

According to a ninth aspect of the invention, in the floating offshorewind turbine of the eighth aspect, the floating body is formed into asubstantially cylindrical shape, a pair of mooring lines composed of twomooring lines whose one ends are connected to two points on acircumference of a circle of the substantially cylindrical shape whenthe floating body is projected onto a horizontal plane is used as themooring method, and the two mooring lines are formed into substantiallytangent lines of the circle and extend on the same side. According tothese aspects, it is possible to suppress rotation around a cylindricalcenter axis of the floating body.

According to a tenth aspect of the invention, in the floating offshorewind turbine of the first aspect, the nacelle is supported by thestructure body such that a predetermined angle is formed between ahorizontal plane and the rotation shaft of the rotor in a state wherewind is not received so that the rotation shaft of the rotor in a statewhere wind is received becomes parallel to a wind direction. Accordingto this aspect, the predetermined angle can be set while taking, intoaccount, a fact that the wind turbine inclines when the rotor receiveswind. Therefore, when electricity is generated, the rotation shaft ofthe rotor can be made parallel to a wind direction. Here, “a state wherethe rotor receives wind and the wind turbine inclines” means a statewhere the wind turbine is inclined by receiving wind of a typical windspeed which is assumed at a place where the wind turbine is installed.Examples of the typical wind speed are an average annual wind speed anda wind speed at which power generating efficiency becomes maximum.

Effect of the Invention

According to the floating offshore wind turbine of the presentinvention, since the yawing suppressing means can suppress yawing causedby a gyro effect, it is possible to suppress adverse influence by theyawing on the power generating efficiency of the wind turbine caused andendurance of devices thereof.

If the nacelle is provided on a windward side as compared with the rotoror a coning angle is given to the rotor, the nacelle can be turned by aso-called weathercock effect, the rotation shaft can be made to conformto a wind direction and the front face of the rotor can be incontradiction to the wind direction. Therefore, it is possible toenhance the power generating efficiency of the wind turbine. Further, itis possible to suppress yawing and to reduce a load of the yawingsuppressing means.

If the hydraulic damper or the friction damper is used as theoscillating control means, resistance of the oscillating control meanscan be varied in accordance with a turning speed of the nacelle.Therefore, it is possible to suppress fast yawing of the nacelle causedby a gyro effect without suppressing slow yawing of the nacelle causedby a weathercock effect.

If the hydrodynamic damper which suppresses yawing by interference withsurrounding fluid is used, resistance can be varied in accordance with aturning speed of the nacelle, the yawing generated in the nacelle or thefloating body due to the gyro effect can be suppressed, pitching of thefloating body can be suppressed, and power generating efficiency andendurance of devices can be enhanced.

The floating offshore wind turbine of the invention includes the yawingsuppressing apparatus. Therefore, it is possible to enhance the powergenerating efficiency and endurance of the devices by suppressing theyawing of the nacelle caused by the gyro effect. It is also possible tosuppress pitching of the floating body by reaction of the gyro effect.

If the floating body is moored by a mooring method which suppressesrotation motion of the floating body around its center axis, it ispossible to effectively suppress yawing of the nacelle and pitching ofthe floating body caused by a gyro effect, and it is possible to enhancepower generating efficiency and endurance of the devices.

If a predetermined angle is provided between a horizontal plane and therotation shaft of the rotor in a state where the rotor does not receivewind, a side view direction of the rotation shaft of the rotor and aside view direction of wind can be substantially parallel to each otherand can be made to substantially conform to each other when electricityis generated. Therefore, a rotation plane of the rotor can be madeperpendicular to a wind direction substantially at right angles, and itis possible to enhance power generating efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing a configuration of afloating offshore wind turbine according to a first embodiment of thepresent invention;

FIG. 2 is a side view of essential portions showing a structure of ayawing suppressing apparatus of a wind turbine according to the firstembodiment of the invention;

FIG. 3 shows a relation between change in a wind direction on the oceanand a deflection angle of a floating body on water caused by influenceof waves, wherein (a) is a graph showing change in a wind direction and(b) is a graph showing change in a deflection angle;

FIG. 4A is a schematic perspective view showing a configuration of ahydraulic damper;

FIG. 4B is a schematic front view showing a configuration of thehydraulic damper;

FIG. 4C is a sectional view taken along a line A-A in FIG. 4B;

FIG. 5A is a schematic perspective view showing a configuration of afriction damper;

FIG. 5B is a schematic front view showing a configuration of thefriction damper;

FIG. 6A is a plan view showing a configuration of a mooring apparatus ofthe floating body according to the first embodiment of the invention;

FIG. 6B is a side view showing a configuration of the mooring apparatusof the floating body according to the first embodiment of the invention;

FIG. 7 is a diagram showing a configuration of a pair of mooring linesin the first embodiment of the invention;

FIG. 8A is a plan view showing a configuration of a conventional tensionmooring method;

FIG. 8B is a side view showing a configuration of the conventionaltension mooring method;

FIG. 9 is a side view of essential portions showing a structure of ayawing suppressing apparatus of a wind turbine according to a secondembodiment of the invention;

FIG. 10A is a schematic side view showing a configuration in a statewhere the yawing suppressing apparatus possessed by a floating offshorewind turbine according to the second embodiment of the inventionreceives wind;

FIG. 10B is a schematic side view showing a configuration in a statewhere the yawing suppressing apparatus possessed by the floatingoffshore wind turbine according to the second embodiment of theinvention does not receive wind;

FIG. 11 is a schematic perspective view showing a configuration of afloating offshore wind turbine according to a third embodiment of theinvention;

FIG. 12 is a schematic perspective view showing a configuration of thefloating offshore wind turbine according to the third embodiment of theinvention; and

FIG. 13 is a schematic perspective view showing a configuration of afloating offshore wind turbine according to a fourth embodiment of theinvention.

EXPLANATION OF SYMBOLS

-   10, 40, 50, 60 floating offshore wind turbine-   11 rotor-   12 rotation shaft-   13 nacelle-   14 turning seated bearing (turning means)-   15 tower (structure body)-   16 yawing suppressing means-   160 hydraulic damper-   165 friction damper-   20, 30 yawing suppressing apparatus-   31 floating body-   32 mooring line-   41 structure body-   42 turning means-   44, 64 hydrodynamic damper-   51A structure body upper portion-   51B structure body lower portion-   α coning angle-   β predetermined angle

MODE FOR CARRYING OUT THE INVENTION

(First Embodiment)

A first embodiment of the present invention will be described below withreference to FIGS. 1 to 8. In this embodiment, a case where theinvention is carried out as a floating offshore wind turbine will bedescribed.

FIG. 1 is a schematic perspective view showing a configuration of thefloating offshore wind turbine 10 according to the first embodiment. Asshown in FIG. 1, the floating offshore wind turbine 10 includes afloating body 31 provided with a yawing suppressing apparatus 20 . Thefloating body 31 is moored to anchors 33 provided on a sea bottom Bthrough mooring lines 32. A line coming out from a lower portion of thefloating body 31 is an electric feeder line 34. A structure of theyawing suppressing apparatus 20 possessed by the floating offshore windturbine 10 of the embodiment will be described with reference to FIG. 2.

FIG. 2 is a side view of essential portions showing a structure of theyawing suppressing apparatus 20 of the wind turbine 10 according to thefirst embodiment. As shown in FIG. 2, the yawing suppressing apparatus20 is composed of a rotor 11 which is rotated by wind, a nacelle 13 inwhich a rotation shaft 12 of the rotor 11 is accommodated, a tower(structure body) 15 having a turning seated bearing (turning means) 14which supports the nacelle 13 such that the nacelle 13 can turn withrespect to a water surface or a ground surface, and a yawing suppressingmeans 16 which suppress yawing of the nacelle 13 with respect to thewater surface.

The rotor 11 includes a hub 17 which is radially provided with aplurality of blades 18, and the rotation shaft 12 connected to the hub17. The rotation shaft 12 is rotatably supported in the nacelle 13. Ifthe rotor 11 receives wind, the rotation shaft 12 rotates and agenerator (not shown) provided in the nacelle 13 generates electricity.A hollow arrow w in FIG. 2 shows a wind direction. In the yawingsuppressing apparatus 20 of the embodiment, the rotor 11 is provided ona leeward side as compared with the nacelle 13. According to thisconfiguration, it is possible to effectively generate a so-calledweathercock effect in which a side view direction of the rotation shaft12 conforms to a wind direction by yawing of the nacelle 13 provided onthe turning seated bearing 14.

The rotation shaft 12 rotates upon receiving wind W, and the rotationshaft 12 is accommodated in the nacelle 13. The nacelle 13 also includeselectricity generating means (not shown) , such as a gear box (notshown) which increases a rotation speed of the rotation shaft 12 andtransmits the rotation to the generator, possessed by a wind turbinedevice. The nacelle 13 is supported by the turning seated bearing 14provided on the tower 15 such that the nacelle 13 can turn in adirection parallel to a sea surface P. According to this configuration,a direction of the rotation shaft 12 can be varied by yawing of thenacelle 13 in accordance with change in a wind direction W, and arotation plane of the blades 18 of the rotor 11 can be in contradictionto wind.

When a force in the vertical direction is applied by waves while therotor 11 is rotating, the yawing suppressing means 16 suppresses yawingof the nacelle 13 generated by a gyro effect. Attention is paid to theyawing of the nacelle 13 caused by the gyro effect, the yawingsuppressing means 16 is provided. Since the yawing suppressing means 16can suppress the yawing of the nacelle 13, it becomes possible toenhance power generating efficiency of the floating offshore windturbine 10 and to enhance endurance of devices thereof. Although thetower 15 is provided with the yawing suppressing means 16 in thisembodiment, instead thereof, the nacelle 13 may be provided with theyawing suppressing means 16.

When the yawing suppressing apparatus 20 is provided on a wind turbineapparatus on land instead of the floating offshore wind turbine 10, thenacelle 13 is supported by the turning seated bearing 14 such that itcan turn with respect to a ground surface. If moment in the verticaldirection is applied for any reason, the yawing suppressing means 16 cansuppress yawing of the nacelle 13. The above-described weathercockeffect is also of assistance in reducing a load of the yawingsuppressing means 16.

Next, a mechanism for generating yawing in the nacelle 13 of thefloating offshore wind turbine 10 by the gyro effect on the ocean willbe described with reference to FIGS. 1 and 3. If a rotating object(substance) rotates in a direction cross at right angles to a rotationaxis, moment acts in directions intersecting with each other at rightangles. This moment is called gyro moment. An effect for generating thegyro moment is called a gyro effect.

Ω×L=T

Ω: angular velocity of pitching motion

L: angular momentum of rotating object

T: gyro moment

When the rotor 11 is rotating motion L, if motion generating a restoringforce via yawing of the floating body 31 by waves of a sea surface P isgenerated, whereby a pitching Ω is generated, the rotor 11 yaws in thevertical direction cross at right angles to the rotation axis S.According to this, gyro moment acts in the horizontal direction cross atright angles to both the rotation axis S of the rotor 11 and thevertical direction. In the floating offshore wind turbine 10, since thenacelle 13 can turn by the turning seated bearing 14, yawing of thenacelle 13 is generated in a direction shown by T in FIG. 1 by this gyromoment.

FIG. 3 shows a relation between change in a wind direction on the oceanand a deflection angle of the floating body on water caused by influenceof waves, wherein (a) is a graph showing change in a wind direction and(b) is a graph showing change in a deflection angle. Portions surroundedby broken lines in the graph (a) as well as the graph (b) show changeduring one hour. If the graphs (a) and (b) of FIG. 3 are compared witheach other, it can be found that change in a wind direction is generatedwhile taking a long time, and change in a deflection angle caused byinfluence of waves is generated in a short time. That is, a turningspeed of the nacelle 13 caused by change in a wind direction is slow,and a speed of yawing of the nacelle 13 caused by a gyro effect causeddue to influence of waves and so on is fast.

Since the deflection angle caused by the influence of waves is variedwith the short period, yawing of the nacelle 13 is induced by the gyroeffect. The yawing of the nacelle 13 adversely affects the powergenerating efficiency of the wind turbine and endurance of the devices.

To selectively suppress yawing of the nacelle 13 caused by the gyroeffect while allowing the nacelle 13 to turn as a wind direction isvaried, it is preferable that means whose resistance is varied inaccordance with a turning speed of the nacelle 13 is used as the yawingsuppressing means 16. According to this, a so-called weathercock effectcan be exerted without generating an attenuation effect for slow yawingof the nacelle 13 supported by the turning seated bearing 14 caused bychange in a wind direction which is varied while taking a relativelylong time. It is possible to allow an attenuation effect to exert foryawing of the nacelle 13 which is caused by waves with a short period,and thus, it is also possible to selectively inhibit yawing of thenacelle 13.

Since the floating offshore wind turbine 10 of the embodiment cansuppress the yawing of the nacelle 13 by the yawing suppressing means16, it becomes possible to suppress the adverse influence.

If the yawing suppressing apparatus 20 including the yawing suppressingmeans 16 is used, it is possible to restrain yawing from generating inthe nacelle 13 by a gyro effect caused by pitching of the floating body31 caused by waves. Further, by suppressing the yawing of the nacelle13, it is also possible to suppress pitching of the floating body 31caused by reaction of the gyro effect.

FIGS. 4A to 4C schematically show a configuration of a hydraulic damper,wherein FIG. 4A is a perspective view, FIG. 4B is a front view and FIG.4C is a sectional view taken along an arrow A-A in FIG. 4B. As shown inthese drawings, the hydraulic damper 160 includes a rotation body 163and oil 164 in its interior surrounded by a body case 161 and a cap 162.The hydraulic damper 160 utilizes a braking force generated by viscosityresistance of the oil 164. By adjusting a gap between the body case 161and the rotation body 163, a contact area of the oil 164 and viscosityof the oil 164, it is possible to vary a braking torque (resistance)with respect to rotation of the rotation body 163. There is such arelation between a rotation speed and a braking torque of the rotationbody 163 that if the rotation speed is increased, the braking torque isincreased, and if the rotation speed is reduced, the braking torque isalso reduced.

If the hydraulic damper 160 is used, since it utilizes the viscosityresistance of oil 164, there is a merit that change with time ofcharacteristics such as wearing is small. It is possible to reduceinfluence of change in viscosity caused by a temperature by selecting akind of oil 164, but it is possible that when wind is strong, heat ofoil 164 is lost, its viscosity is increased and the braking torque isincreased by taking a constitution of cooling oil 164 by wind as anexample.

FIGS. 5A and 5B schematically show a configuration of a friction damper,wherein FIG. 5A is a perspective view and FIG. 5B is a front view. Asshown in these drawings, the friction damper 165 includes a frictionmaterial 167 which is in contact with an outer surface of a rotationshaft 166, a rotation shaft-connecting material 168 which surrounds thefriction material 167, and an elastic body 169 which pushes the rotationshaft-connecting material 168 in a predetermined direction. The frictiondamper 165 utilizes a braking force generated by friction resistancebetween the rotation shaft 166 and the friction material 167. Byadjusting friction resistance and contact areas between the rotationshaft 166 and the friction material 167, it is possible to vary abraking torque (resistance). There is such a relation between a rotationspeed and a braking torque of the rotation shaft 166 that if therotation speed is increased, the braking torque is increased, and if therotation speed is reduced, the braking torque is also reduced.

When the friction damper 165 is used, there are merits that a sealingportion is unnecessary and thus the configuration can be simplified, andin an environment that an ambient temperature is largely varied,characteristics can relatively stably be maintained. Even if a size ofthe friction material 167 is varied due to wearing, a braking force canconstantly be maintained correspondingly by means of a biasing force ofthe elastic body 169. That is, even if the size of the friction material167 is varied due to friction, the elastic body 169 biases the frictionmaterial 167 and friction resistance between the rotation shaft 166 andthe friction material 167 can constantly be maintained.

The floating body 31 is moored to the anchors 33 provided on the seabottom B by means of the mooring lines 32 in water by a mooring methodof restraining the floating body 31 from rotating around the centeraxis. Hence, rotation of the floating body 31 in water is suppressed.This mooring method will be described later.

There is a floating offshore wind turbine including an apparatus whichactively controls rotation of the nacelle to conform to a winddirection. In this facility, a wind turbine is temporalily fixed to thefloating body and held at a position conforming to the wind direction,i.e., a position where a rotation plane is in contradiction to wind.Hence, the floating body tries to rotate around a vertical rotation axisby gyro moment caused by a gyro effect of the rotor of the wind turbine.Therefore, a mooring method which suppreses rotation motion of thefloating body around its center axis suppresses this yawing. Accordingto this, it is possible to suppress the adverse influence on the powergenerating efficiency of the floating offshore wind turbine andendurance of the devices thereof.

However, there is another floating offshore wind turbine of a method inwhich the apparatus which actively controls rotation of the nacelle isomitted and a nacelle is made to conform to a wind direction by aweathercock effect. In such a facility, a rotation shaft of a rotor of awind turbine is supported such that the rotation shaft can freely turnwith respect to a floating body. Hence, even if yawing of the floatingbody is suppressed, yawing caused by a gyro effect generated in thenacelle can not be suppressed. Therefore, in the floating offshore windturbine 10 of this embodiment, the yawing suppressing means 16 isprovided, thereby suppressing the yawing generated in the nacelle 13 bythe gyro effect.

The mooring method of restraining the floating body 31 from rotatingaround its rotation axis will be described with reference to FIGS. 6A,6B and 7.

FIGS. 6A and 6B show a configuration of a mooring apparatus of thefloating body according to the first embodiment, wherein FIG. 6A is aplan view and FIG. 6B is a side view. Here, in FIG. 6A, the mooringapparatus of the floating body is projected onto a horizontal plane. Oneends of the plurality of mooring lines 32 are connected to the floatingbody 31. The other ends of the mooring lines 32 are connected to theanchors 33 provided in water.

The floating body 31 is formed into a substantially cylindrical shape. Apair of mooring lines composed of the two mooring lines 32 is used. Oneends of the two mooring lines 32 are connected to two points on acircumference of a circle of the substantially cylindrical shape whenthe floating body 31 is projected onto the horizontal plane. The twomooring lines 32 are formed into substantially tangent lines of thecircle, and the mooring lines 32 extend on the same side. According tothis, it is possible to avoid a case where when the yawing suppressingmeans 16 suppresses yawing, a force is applied to the floating body 31and yawing is generated in the floating body 31.

FIG. 7 shows a relation between the floating body 31 and the two mooringlines 32 connected to lower right anchors 33 in the plan view(projection view on horizontal plane) of FIG. 6A. One ends of the twomooring lines 32 are connected to points A and B on the circumference ofthe floating body 31. The mooring lines 32 are formed into tangent linesL1 and L2 in the points A and B.

In this configuration, when rotation around a center C of the floatingbody 31 is generated in the floating body 31, one of the two mooringlines 32 extends and a tensile force acts. When a radius of the floatingbody 31 is defined as r and a rotation angle of the floating body 31 isdefined as Δθ, an extension amount ΔL of the mooring line 32 on theextension side in this plan view is obtained by the following equation(1):ΔL=r×Δθ . . .   (1)

In this case, if a spring rate of the mooring line 32 is defined as k, atensile force T of the floating body 31 in a tangential direction isobtained by the following equation (2) by Hooke's law:T=k·ΔL . . .   (2)

A torque N generated by this extension is obtained by the followingequation (3):N=T·r . . .   (3)

If configurations of the two mooring lines 32 are as shown in FIG. 7, atorque which rebels against rotation can be generated irrespective of arotation direction. Hence, rotation of the floating body 31 issuppressed.

In FIGS. 6A and 6B, the mooring lines 32 are formed into the tangentlines L1 and L2 in FIG. 7. However, it is apparent that even if themooring lines 32 are formed into L3 and L4 (broken lines) in FIG. 7, thesame effect can be exerted.

FIGS. 8A and 8B show a configuration of a conventional simple tensionmooring method. It is apparent that motion (floating motion) of thefloating body 31 in the horizontal direction is suppressed by mooringlines 32 which radially extend in three directions shown in FIG. 8.However, in the plan view (FIG. 8A), since an angle formed between arotation direction (circumferential direction) of the floating body 31and the mooring line 32 is substantially 90°, it is difficult tosuppress the rotation. Hence, the mooring method shown in FIGS. 8A and8B does not suppress rotation of the floating body 31 around its centeraxis.

(Second Embodiment)

A second embodiment of the invention will be described below withreference to FIG. 9. A yawing suppressing apparatus of a wind turbine ofthe second embodiment is different from the yawing suppressing apparatusof the first embodiment in a configuration where a coning angle is givento a rotor. The same numbers are allocated to the members described inthe first embodiment, and explanation thereof will be omitted in thesecond embodiment.

FIG. 9 is a side view of essential portions showing a structure of theyawing suppressing apparatus 30 of the wind turbine according to thesecond embodiment. As shown in FIG. 9, according to the yawingsuppressing apparatus 30 of the embodiment, a nacelle 13 is provided ona windward side as compared with a rotor 11. A coning angle α is givento the rotor 11. Here, the coning angle α is an angle between a straightline which connects a connected portion 18A of a blade 18 with respectto a hub 17 and a tip end 18B and which is shown by an alternate longand short dash line and a vertical line V shown by an alternate long andshort dash line in the drawing.

According to this configuration, the nacelle 13 supported by a turningseated bearing 14 is automatically turned in accordance with change of awind direction W in a state where the nacelle 13 can freely turn in thehorizontal direction, and a weathercock effect for conforming a rotationshaft 12 of a rotor 11 to the wind direction can be enhanced. When anaxial direction of the rotation shaft 12 and a wind direction conform toeach other, a rotation plane of the rotor 11, i.e., a plane formed by alocus of the tip end 18B of the blade 18 is perpendicular to the winddirection substantially at right angles. If the weathercock effect isenhanced, a load of yawing suppressing means 16 is further reduced.

When the present invention is carried out as the floating offshore windturbine (see FIG. 1) including the yawing suppressing apparatus 30, itis preferable to employ such a configuration that the rotation shaft 12of the rotor 11 in an electricity generating state where the rotationshaft 12 receives wind and inclines is located on a horizontal plane H.This configuration will be described with reference to FIGS. 10A and10B.

FIGS. 10A and 10B schematically show a configuration of the yawingsuppressing apparatus 30 provided in the floating offshore wind turbineof the embodiment, wherein FIG. 10A is a side view in a state where windis received and FIG. 10B is a side view in a state where wind is notreceived. As shown in FIG. 10A, according to the yawing suppressingapparatus 30 of the embodiment, the rotation shaft 12 (straight line inthe axial direction is shown by S) of the rotor 11 in the electricitygenerating state where the rotation shaft 12 receives wind and inclinesis located on the horizontal plane H. According to this, a direction ofthe rotation axis of the rotation shaft 12 can conform to the winddirection W (both of them can be parallel to each other). Hence, in thestate where wind is not received as shown in FIG. 10B, the nacelle 13 issupported by a tower 15 such that the rotation shaft 12 (straight lineS) of the rotor 11 forms a predetermined angle β with respect to thehorizontal plane H.

The predetermined angle β may be set based on the most general windspeed so that power generating efficiency of the floating offshore windturbine becomes excellent. Further, control means of the predeterminedangle β which varies the predetermined angle β such that thepredetermined angle β becomes the optimal angle in accordance with awind speed may be provided.

The configuration described with reference to FIGS. 10A and 10B can alsobe used in the floating offshore wind turbine using the yawingsuppressing apparatus 20 described in the first embodiment.

(Third Embodiment)

A third embodiment of the invention will be described below withreference to FIGS. 11 and 12. In the third embodiment, a case where theinvention is carried out as a floating offshore wind turbine will bedescribed. The same numbers are allocated to the members described inthe first or second embodiment, and explanation thereof will be omittedin the third embodiment.

FIG. 11 is a schematic perspective view showing a configuration of afloating offshore wind turbine 40 according to the third embodiment. Asshown in FIG. 11, the floating offshore wind turbine 40 is configuredsuch that a nacelle 13 and a structure body 41 are integrally formedtogether so that the nacelle 13 does not turn with respect to thestructure body 41. The structure body 41 floats on water, the nacelle 13is fixed to an upper end of the structure body 41, and a lower end ofthe structure body 41 is connected to anchors 43 provided on a seabottom B through turning means 42. The turning means 42 is forconnecting the structure body 41 to the anchors 43 such that thestructure body 41 can turn in accordance with change in the winddirection W, and the turning means 42 makes the structure body 41 exerta weathercock effect.

Hydrodynamic dampers 44 are provided on an outer side of the structurebody 41. The structure body 41 is moored by a mooring method which doesnot suppress rotation of the structure body 41 around its center axis.By locating the hydrodynamic dampers 44 in water, a function as yawingsuppressing means can be exerted. That is, resistance of each of thehydrodynamic dampers 44 having a blade shape against water becomessmaller with respect to slow yawing of the structure body 41 and becomesgreater with respect to fast yawing. Hence, it is possible toselectively attenuate and suppress the yawing of the structure body 41caused by a gyro effect which is fast yawing. By providing the structurebody 41 with the hydrodynamic dampers 44 in this manner, it is possibleto suppress yawing of the structure body 41 caused by a gyro effect. Tosuppress yawing of the structure body 41, the structure body 41 may beprovided with the hydraulic damper 160 (see FIGS. 4A to 4C) or thefriction damper 165 (see FIGS. 5A and 5B). It is also possible to moorthe structure body 41 also using another mooring method which does notsuppress rotation of the structure body 41 around its center axis bymeans of mooring lines.

Although the hydrodynamic dampers 44 are applied to the floatingoffshore wind turbine in the third embodiment, it is also possible toapply the hydrodynamic dampers 44 to a wind turbine installed on theground for example. In this case, turning means is supported in a statewhere the structure body floats in water in a pool such that thestructure body can turn with respect to a ground surface, and the waterin the pool provided in a periphery and the hydrodynamic dampers 44 aremade to mutually interfere. According to this, the hydrodynamic dampers44 can exert function as yawing suppressing means also in the windturbine installed on the ground.

FIG. 12 is a schematic perspective view showing a configuration of afloating offshore wind turbine 50 having a configuration different fromthat of the floating offshore wind turbine 40 according to the thirdembodiment. As shown in FIG. 12, in the floating offshore wind turbine50, an upper portion 51A of a structure body 51 and the nacelle 13 areintegrally formed together, and the turning means 42 is provided betweenthe structure body upper portion 51A and a structure body lower portion51B. The structure body lower portion 51B located lower than the turningmeans 42 is fixed to the anchors 43 on the sea bottom B through aplurality of mooring lines 54.

According to this configuration, since the structure body upper portion51A can turn in accordance with change of the wind direction W by theturning means 42, it is possible to exert a weathercock effect. Theyawing suppressing means 16 provided in the structure body 51 cansuppress yawing of the nacelle 13 by a gyro effect. It is also possibleto moor the structure body upper portion 51A also using another mooringmethod which does not suppress rotation around a center axis by means ofmooring lines.

(Fourth Embodiment)

A fourth embodiment of the invention will be described below withreference to FIG. 13. In the fourth embodiment, a configuration in whicha floating offshore wind turbine is moored by a mooring method that doesnot suppress rotation of a floating body around its center axis will bedescribed. The same numbers are allocated to the members described inthe first to third embodiments, and explanation thereof will be omittedin the fourth embodiment.

FIG. 13 is a schematic perspective view showing a configuration of afloating offshore wind turbine according to the fourth embodiment. Asshown in FIG. 13, a floating body 31 of a floating offshore wind turbine60 of the fourth embodiment is moored to a sea bottom B by mooring lines32 by means of a so-called catenary method. Therefore, the floating body31 can yawing around its center axis to some extent. That is, thefloating body 31 is moored by a mooring method not suppressing rotationaround its center axis. Hence, even if the yawing suppressing means 16constrains yawing of a nacelle 13 with respect to the floating body 31generated by a gyro effect, the floating body 31 can yawing around itscenter axis to some extent. As a result, the mooring lines 32 can notsuppress the yawing of the nacelle 13. However, the floating body 31 ofthe floating offshore wind turbine 60 is provided with a plurality ofblade-shaped hydrodynamic dampers 64. The hydrodynamic dampers 64 canrestrain the floating body 31 from generating the yawing.

When the floating offshore wind turbine is moored by the mooring methodwhich does not suppress rotation of the floating body around its centeraxis, if the yawing suppressing means 16 which is for suppressing yawingof the nacelle 13 in the turning seated bearing 14 and the hydrodynamicdampers 64 which are for suppressing yawing of the floating body 31 arecombined with each other, it is effective for suppressing yawing of thenacelle 13 and the floating body 31 caused by a gyro effect.

In the floating offshore wind turbine 60 of the fourth embodiment, thetwo hydrodynamic dampers 64 are disposed such that they are opposed toeach other through the floating body 31. That is, a line connectingmounted portions of the two hydrodynamic dampers 64 to the floating body31 passes a substantially center of a cross section which is parallel toa horizontal plane of the floating body 31. This is because that thehydrodynamic dampers 64 are provided not for suppressing pitching of thefloating body 31 but for suppressing yawing of the floating body 31.That is, the hydrodynamic dampers 64 of the floating offshore windturbine 60 are provided so that the hydrodynamic dampers 64 interferewith outside water and become resistance of yawing of the floating body31. Therefore, it is unnecessary to provide three or more hydrodynamicdampers 64 unlike a case where the hydrodynamic dampers 64 are providedfor suppressing the pitching. Hence, even if the number of hydrodynamicdampers 64 is one, the same function is exerted. However, since the samefunction is exerted eve if the number of the hydrodynamic dampers 64 isthree or more, the number of the hydrodynamic dampers 64 may be three ormore.

In the fourth embodiment, even if an apparatus which actively controlsrotation of the nacelle is provided instead of the yawing suppressingmeans 16, it is possible to restrain the floating body 31 fromgenerating yawing by the hydrodynamic dampers 64. The hydrodynamicdampers 64 generate a hydrodynamic effect by interference withsurrounding fluid and exert a function as yawing suppressing means.Hence, a shape of a cross section of the structure body itself may be anangular shape or a shape having many concavo-convex portions.

INDUSTRIAL APPLICABILITY

The present invention can be utilized as an apparatus for enhancingpower generating efficiency of a wind turbine and endurance of devicesthereof. Especially, the invention is useful for enhancing powergenerating efficiency of a floating offshore wind turbine and enduranceof devices thereof.

The invention claimed is:
 1. A floating offshore wind turbine whichgenerates electricity using a floating body as a portion of a structurebody on ocean, comprising: a rotor which is rotated by wind, a nacellein which at least a rotation shaft of the rotor is accommodated, whereinthe structure body is in shape of a tower, includes a turning seatedbearing which supports the nacelle such that the nacelle can turn withrespect to a water surface, a hydrodynamic damper, which is provided onthe structure body and suppresses yawing of the nacelle with respect tothe water surface by mutual interference between a blade-shapedstructure provided directly in a lower part of the structure body andperipheral fluid, a hydraulic damper or friction damper, which isprovided between the nacelle and the structure body where thehydrodynamic damper is provided and suppresses the yawing of thenacelle, and a plurality of mooring lines with which the structure bodyis moored to anchors on a bottom of water.
 2. The floating offshore windturbine according to claim 1 wherein the nacelle is provided on awindward side as compared with the rotor.
 3. The floating offshore windturbine according to claim 2, wherein a coning angle is given to therotor.
 4. The floating offshore wind turbine according to claim 1,wherein the floating body is formed into a substantially cylindricalshape, the plurality of mooring lines are composed of pairs of mooringlines whose one ends are connected to two points on a circumference of acircle of the substantially cylindrical shape and the pairs of mooringlines are formed into substantially tangent lines of the circle andextend on the same side when the floating body is projected onto ahorizontal plane.
 5. The floating offshore wind turbine according toclaim 1, wherein the nacelle is supported by the structure body suchthat a predetermined angle is formed between a horizontal plane and therotation shaft of the rotor in a state where wind is not received sothat the rotation shaft of the rotor in a state where wind is receivedbecomes parallel to a wind direction.